The Collaborative International Dictionary of English v.0.48:

Cardamom \Car"da*mom\ (k[aum]r"d[.a]*m[u^]m), n. [L. cardamomun,
   Gr. karda`mwmon]
   1. The aromatic fruit, or capsule with its seeds, of several
      plants of the Ginger family growing in the East Indies and
      elsewhere, and much used as a condiment, and in medicine.
      [Also spelled cardamum.]

   Syn: cardamon.
        [1913 Webster]

   2. (Bot.) A rhizomatous herb which produces cardamoms, esp.
      Elettaria Cardamomum and several species of Amomum.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cardamom
    n 1: rhizomatous herb of India having aromatic seeds used as
         seasoning [syn: cardamom, cardamon, Elettaria
         cardamomum]
    2: aromatic seeds used as seasoning like cinnamon and cloves
       especially in pickles and barbecue sauces [syn: cardamom,
       cardamon, cardamum]